Microfabrication using photolithography techniques has conventionally been performed in manufacturing of semiconductor devices. The microfabrication is a process of forming a thin film of a photoresist composition on a substrate to be processed such as a silicon wafer, irradiating the film with active light such as ultraviolet rays through a mask pattern having semiconductor device patterns, developing the pattern, and etching the substrate to be processed such as a silicon wafer using the resulting photoresist pattern as a protection film. With the increasing density of semiconductor devices in recent years, the active light used have been changed to those at shorter wavelengths from KrF excimer laser (248 nm) to ArF excimer laser (193 nm). Accordingly, the effects of diffuse reflection or standing waves of active light from the substrate become a serious issue, and a method has been widely adopted in which an anti-reflective coating (Bottom Anti-Reflective Coating, BARC) is provided as a resist underlayer film between the photoresist and the substrate to be processed for serving the function of preventing reflection.
Known examples of the anti-reflective coatings include: inorganic anti-reflective coatings such as titanium, titanium dioxide, titanium nitride, chromium oxide, carbon, and α-silicon; and organic anti-reflective coatings made from a light absorbing substance and a polymer compound. In forming films, the former requires systems such as a vacuum deposition system, a CVD system, and a sputtering system, whereas the latter requires no special system. In this respect, organic anti-reflective coatings are advantageous and a number of studies have been conducted.
ArF immersion lithography in which exposure is performed through water has been actively examined as a next-generation photolithography technique that replaces the photolithography technique using ArF excimer laser (193 nm). The photolithography techniques using light, however, have been approaching their limits. EUV lithography technique using EUV (at a wavelength of 13.5 nm, extreme ultraviolet) has been attracting attention as a new lithography technique after the ArF immersion lithography.
In the device fabrication process using EUV lithography, a substrate coated with an EUV resist is exposed by EUV radiation and developed to form a resist pattern. Here, in order to protect the EUV resist from contaminants or block undesired radiation such as UV light or DUV (deep ultraviolet) light, a method has been disclosed, in which the overlayer on the EUV resist includes a polymer including a group containing at least one of beryllium, boron, carbon, silicon, zirconium, niobium, and molybdenum (Patent Document 1 and Patent Document 2).